Lime, Pac, Polymer Usage of Textile Waste Water

Use more fish hooks.

You need a specialist in-house to investigate. If you haven't got one, hire one.

Get a bmoc system and use 75% bmf to up the cod to match your sbc.

Or, blow harder.

Probably goes back to the original design of the system.

Has the throughput gone beyond design level? Are there additional COD loads beyond the original design brief? etc.

There might be methods to increase transfer (blow harder, smaller bubbles, longer residence time etc.) that will help your outcome.

Need a professional expert to assess.

Might even need to review whether addition of "bugs" into the system would help.

Maybe you should have done a study on the biotoxicity of the C.O.D. including whatever new chemical(s) you introduced, that stunted the population of aerobic organisms! Go back the the beginning, and hire a competent consultant who can manage the newly formulated problem into a complete answer with results!